Electrophysiologic study (EPS) in a patient with atrioventricular nodal reentrant tachycardia and dual AV nodal pathways

The tracing shows three surface ECG leads (I, II, V1) and intracardiac recordings from the high right atrium (HRA), bundle of His (HIS), right ventricular apex (RVA), and coronary sinus (CS). During atrial pacing (S1) at a cycle length of 600 milliseconds (100 beats per minute), the AH interval is 120 milliseconds. An atrial premature beat (S2) is added at a coupling cyle of 420 milliseconds; this results in a prolongation of the PR interval and increase in the AH interval to 184 milliseconds.